In the current global economy, the United States is in competition for non-renewable resources. In this country and Minnesota in particular, aggregate materials are being depleted at a rapid pace. Environmental stewardship will continue to be more restrictive along with permitting criteria. It is becoming increasingly important to investigate the use of recycled materials in pavement construction. Minnesota has had a long history of using recycled materials in pavement construction. Recycled materials have been used in all layers of the pavement, from the surface down to the unbound supporting layers. Mn/DOT¿s current Class 7 specification (Spec 3138) allows salvaged or recycled HMA, PCC, and glass to be used as part of the granular base materials. However, their material properties (strength, stiffness, unsaturated properties, etc.) are not well understood. Under the current design procedures, Class 7 materials are assigned the same empirical properties as a typical Class 5 (gravel) material. New mechanistic-empirical design procedures require more detailed material properties in order to accurately predict pavement performance. In addition, the use of crushed concrete in particular has raised some environmental concerns. These concerns have focused on the relatively high pH of the effluent produced by drainage systems that remove water from untreated recycled concrete aggregate foundation layers. Also of concern is the identification of some constituents (arsenic, chromium, aluminum, and vanadium) that are considered hazardous in drinking water. Related studies include: - NCHRP 4-31: Tests of Recycled Aggregates for Use in Unbound Pavement Layers - recommend procedures for performance-related testing and selection of recycled HMA and PCC materials for use as aggregates in unbound pavement layers, singularly or in combination with other materials (currently underway - ERES) - RMRC Project 6 - Evaluation of Tests for Recycled Material Aggregates for Use in Unbound Applications - evaluating potential aggregate materials other than reclaimed HMA and PCC (currently underway - New Hampshire) - Sensitivity Analysis of Flexible Pavement Response and AASHTO 2002 Design Guide to Properties of Unbound Layers - compared predictions and field response calculated from isotropic and anisotropic models; results from the 2002 DG model surprisingly showed that base properties did not influence deformation (ICAR Report 504-1, 2004 - Texas A&M). - Use of Crushed Concrete Products in Minnesota Pavement Foundations - studied environmental and performance concerns and provided recommendations for revisions to current specifications (Mn/DOT Report 96-12, 1996 - Mark Snyder) - LRRB 812: Resilient Modulus & Strength of Base Course with Recycled Asphalt - investigate the criteria for using recycled materials with respect to resilient modulus and strength of laboratory specimens (currently underway - University of Minnesota) Most of the current and former research projects using recycled materials are based on laboratory material characterization and mix design. The research proposed in this pooled fund study seeks to validate many of the previous findings with field performance data. The design guide modeling performed at Texas A&M is also in need of field validation. There is some anecdotal evidence of existing recycled base materials, but this research would provide a controlled field experiment in which quantifiable results could be obtained. This research would also provide a good opportunity to revisit some of the environmental concerns and address ways to mitigate the ill effects of effluent from the recycled concrete base layer. This research will help broaden the application of mechanistic-empirical pavement design methods to the use of recycled materials.

The objective of this study is to monitor the performance of several test cells at the Minnesota Road Research Facility (MnROAD) constructed using recycled materials in the granular base layers, including blended with virgin materials and 100% recycled asphalt and concrete pavement materials. The material properties will be monitored during construction and throughout the pavement life in order to determine their effects on pavement performance. The properties will be used to verify mechanistic-empirical design inputs, especially their variation with changing seasons and moisture regimes. This pooled fund study is strictly to perform the recycled materials research on newly built test sections at MnROAD, and its funding will come from Mn/DOT and other participating states. The funding for initial construction of the test sections will be obtained separately from Mn/DOT and other partners.

This project is expected to consist of the following activities: - Work Plan: The work plan for this pooled fund study will be developed by the participating organizations. This will include selecting recycled materials to construct the base layer for 3 cells at MnROAD. Possibilities include: o 100% crushed concrete o crushed concrete blended with virgin aggregate o RAP blended with virgin aggregate The pavement surface must also be carefully selected for these sections. Ideally, the same pavement will cover all three cells so as to minimize variables in the experiment. - Instrumentation Design: Thermocouples, TDRs (moisture), strain gages, etc. - General Testing & Monitoring: Monitor the pavement performance over time on each test section. Monitoring activities will include FWD tests, rutting measurements, distress surveys, ride measurements, and analysis of pavement sensor data. - Special Testing & Monitoring: Unsaturated soil properties, resilient modulus, seasonal variation of material properties, etc. - Design Guide Modeling & Validation: The material properties for recycled unbound layers will be modeled in the new mechanistic-empirical design procedure. - Pooled Fund Travel: Money for each state to travel to discuss the progress of the study. - Data Analysis & Reports: Work done under a research contract will develop interim and final reports that document the findings of this study.

Mn/DOT along with other participating states are asked to contribute $15,000 per year for 5 years to fund the research proposed in this pooled fund study. The Minnesota Department of Transportation (as the lead agency) along with other partners will provide approximately $200,000 in construction funding outside of this pooled fund study to construct the pavement test sections using recycled materials.